In modern vehicles, the battery is of essential importance as an energy store not only for the operation of the vehicle, such as starting, but increasingly also as a store for regained energy, such as for brake energy storage.
To ensure the operational security required for this, there must be the possibility of being able to determine the internal states of the battery. They can normally be determined by factors such as the following:
Current charge state (SoC), aging state (SoH) and, for special main functions, degree of function satisfaction (SoF).
Previously known systems for the determination of the battery state include sensors which use measured current values, voltage values and temperature values as the input values for an internally simulated battery model. A disadvantage of these battery models consists of the fact that they are relatively inexact, which is due to the complexity of these models in particular in connection with the generally used lead acid batteries and to the limited means for the calculation which are made available by the integrated system including the respective models. The respectively required compromise between the required complexity and the system costs frequently takes place at the cost of the achievable performance.
In EP 1 632 782 A1 so-called impedance spectroscopy is described as the method for the determination of the battery states which is based on an analysis of the spectrum of the internal impedance of the battery to be inspected. This requires a specific test by means of a frequency sweep excitation for the obtaining of the impedance profile, whereby the use of this method was previously restricted to a stationary test device.
A monitoring system of the initially named kind is known from U.S. Pat. No. 4,678,998. In this known system, the required different frequency components in the battery current are generated by electrical consumers of the respective vehicle connected to the battery. It is of disadvantage in this connection that the respective excitation taking place via the electrical consumers is not controlled and accordingly the desired frequency components are not generated in every case.